Emergence of a stem-like state in the tumor and adaptation to host immune defenses are in large part responsible for disease progression and recurrence in cancer patients. Thus, to reduce the mortality rate due to cancer, it is important understand the manner through which the tumor acquires a stem-like state and through which it evades immune surveillance. We recently found that during immune selection, cancer cells gain expression of Nanog, a master transcription factor pivotal in the maintenance and self-renewal of pluripotent stem cells. Nanog confers a stem-like and immune-resistant phenotype to these cancer cells, and inhibition of Nanog leads to tumor eradication by CD8+ cytotoxic T lymphocytes (CTLs) in mice. Furthermore, we found that Nanog is abundant in a wide variety of human cancer types, and Nanog expression in tumor tissue correlates with stage of disease and overall survival of patients with cervical neoplasia. Our studies thus far have identified Nanog as a prime molecular target for cancer therapy and suggest a link between the stem- like state in cancer and immune surveillance. The purpose of the current project is to investigate the role of Nanog in tumor immune escape. We hypothesize that cancer cells undergo evolution towards Nanog expression in the natural course of host immune surveillance, and that Nanog creates a microenvironment that protects the tumor from attack by CTLs. Our specific aims are to: (1) Characterize tumor evolution towards Nanog expression in real-time in live animals during an anti-tumor immune response; (2) Characterize the role of Nanog in setting up an immune-suppressive tumor microenvironment; and (3) Characterize the molecular mechanisms through which Nanog coordinates immune escape. The successful implementation of this project will introduce a platform technology to explore tumor evolution at the molecular level in real-time and provide key insight into the mechanisms that mediate tumor adaptation in the natural setting of the host immune system. Also, this project introduces and evaluates the concept that the stem-like phenotype of cancer may arise through immune surveillance and mediate immune escape. The results of this study will have significant implications for the clinical diagnosis and management of cancer.